The Squamata, or the scaled reptiles, are the largest recent order of reptiles, comprising all lizards and snakes. With over 10,000 species, it is also the second-largest order of extant vertebrates, after the perciform fish, and roughly equal in number to the Saurischia (one of the two major groups of dinosaurs). Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the neurocranium. This is particularly visible in snakes, which are able to open their mouths very wide to accommodate comparatively large prey. They are the most variably sized order of reptiles, ranging from the 16 mm (0.63 in) dwarf gecko (Sphaerodactylus ariasae) to the 5.21 m (17.1 ft) green anaconda (Eunectes murinus) and the now-extinct mosasaurs, which reached lengths of 14 m (46 ft). Among the other reptiles, squamates are most closely related to the tuatara, which strongly resembles lizards.
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